Unprotected wood structures are susceptible to degradation by fungi and insects such as termites, which can cause substantial damage to wood building structures. Property damage in US alone is estimated to be in the neighborhood of 1 billion dollars a year. Various processes and chemicals have been used to treat wood to protect it from insect degradation. For example, preservatives, such as Copper Chrome Arsenate (CCA), ACC, ACQ and borate, have been impregnated in wood by a variety of processes. One popular method of integrating chemicals in the wood is by a vacuum/pressure treatment in the presence of an aqueous solution containing the preservative.
While the known methods are relatively successful at introducing preservatives in wood products, the resulting product is very prone to wash out by exposure to water. In particular, borate treated lumber is particularly prone to wash-out by rain water and cannot be used in exterior structures. Methods have been developed to attempt preventing the leaching out of preservatives. One such method is described in U.S. Pat. No. 6,426,118 to Barnisin. The method consists in drying the wood before infusing the preservative followed by further drying and the infusion of a waxy solid that constitutes a barrier to water and prevent leaching of the active ingredient. This method suffers from the need to treat the wood with not only the active ingredient but also the waxy solid which makes the treatment longer and more costly. Furthermore the wax may adversely affect further treatment of the wood with coatings such as paint.
Another example is provided in Du Fresne et al. U.S. Pat. No. 3,306,765 which teaches the addition of carbon dioxide under pressure to borate treated wood to fix fireproofing agents. This method requires chemical treatment in addition to borate treatment which increases the cost of treatment and may impact the mechanical property of wood.
Therefore, there is need for a better process for preventing preservatives leaching out of wood.